Obesity is often associated with insulin resistance and abnormal production of inflammatory cytokines. Central obesity represents a major risk for the development of type 2 diabetes mellitus (T2DM) and cardiovascular complications. Adipose tissue and especially omentum (adipocytes and resident macrophages) release several cytokines. Bariatric surgery and specifically Roux-en-Y gastric bypass (RYGB) is the only modality that results in sustained weight loss. Our studies and those of others demonstrate that RYGB is effective in reversing T2DM in a high proportion of patients. The mechanisms remain unknown. We have evidence showing that weight loss after surgery is not the sole mechanism behind the metabolic improvements. The improvements occur very early (within 10 days) post-op and precede any significant weight loss; they are related to visceral fat distribution and are racially biased, with African Americans showing blunted and more delayed responses than Caucasians. The central hypotheses of this application is that improvements in insulin sensitivity after bariatric surgery are racially biased and begin early in the postoperative period (10-30 days) and are mediated by changes in the secretion of energy-related peptides, while the long-term effects (greater than 1 month) are mediated by down-regulation of inflammatory factors. Additionally, we hypothesize that the removal of the omentum in combination with bariatric surgery enhances the reversal of the insulin resistance and will diminish the racial differences in response to bariatric surgery. We propose a randomized study in Caucasian and African American morbidly obese patients to evaluate changes in glucose and fatty acid metabolism. Patients will be randomized to two groups, one with RYGB alone and the second with RYGB with omentectomy. Three specific aims are proposed. In Specific Aim 1, we will determine the mechanism for the metabolic improvements after RYGB. Specifically, we will examine alterations in the secretion and action of energy related peptides and inflammatory responses. Specific Aim 2 explores the mechanism for the blunted/delayed metabolic improvement after RYGB in African American patients. We will examine the genetic basis for differences in the two races using microarray analysis of muscle and visceral and peripheral adipose tissues. We will explore the role of resident macrophages in mediating associated inflammatory responses. Specific Aim 3 will determine if combining omentectomy with RYGB accelerates and sustains improvements especially in the African American population. The studies include determination of regional fat stores, adipocyte size, tissue macrophage content and macrophage gene expression, diurnal and food-induced secretion of adipokines (leptin, resistin and adiponectin) and of energy regulating-peptides such as ghrelin and PYY. Parameters will be correlated with time dependent changes in inflammatory markers (e.g. CRP, IL-6, TNF-a2R, etc.) and with tissue insulin responsiveness using hyperinsulinemic euglycemic clamps.